1. Field of the Invention
The present invention generally relates to a component part sorting and selection method and apparatus, and more particularly, to a method and apparatus for sorting and selecting component parts from a component part inventory to be used in the manufacture of a device so as to increase the utilization efficiency of the component inventory while at the same time substantially improving device yields. The invention is particularly suited to the manufacture of devices such as optical amplifiers formed from a number of discrete components each having a measured insertion loss.
2. Description of the Related Art
An optical amplifier is manufactured by assembling multiple components within an optical cassette. As shown in FIG. 1, the amplifier may include, for example, a tap 101, an isolator 102, a 1480 WDM (wave division multiplexer) 103, a 1550/1625 WDM 104, an isolator 105, a 980 WDM 106, an isolator 107 and a tap 108. An optical coupler 100 is positioned at the front end of the tap 101.
When the amplifier of FIG. 1 is to be manufactured, design specifications dictate a so-called "loss budget", i.e., a maximum end-to-end insertion loss. The actual end-to-end insertion loss will roughly equal the sum of the insertion losses of the components making up the amplifier. An amplifier which exceeds the loss budget is not acceptable and is either discarded or disassembled for recycling of parts. A typical loss budget for an optical amplifier is on the order of 3.5 dB.
The manufacturer of the amplifier builds an inventory of components by purchasing batches of the components from suppliers, each batch having a specified loss distribution. For example, as shown in FIG. 2, the insertion losses of a batch of 250 optical isolators may take on a bell-curve distribution with a mean of 0.38 dB. The price of each batch of components needed to construct the optical amplifier is negotiated at least partly based on its loss distribution. The further the loss distribution is located towards 0 dB, the more expensive the batch, and visa versa.
Suppose, for example, that isolators are required each having a loss of no more than about 0.38 dB. While the manufacturer can certainly purchase a batch of isolators having a loss distribution completely within the 0.38 dB limit (i.e., the entire bell curve falling below 0.38 dB), such would generally be cost prohibitive and would result in a large number of amplifiers being "overbuilt". That is, suppose further that each of the nine components forming the amplifier were purchased on the same basis. All resultant amplifiers would have an end-to-end insertion loss well below the loss budget. While this may be acceptable from an engineering point of view, it is not an economically sound practice. Thus, the manufacturer instead purchases a batch of isolators having a mean insertion loss of around 0.38 dB (such as that shown in FIG. 2), knowing that the isolators falling in the upper half of the bell curve exceed the desired maximum loss.
After building an inventory of batches of each component, the optical amplifiers are assembled, typically by selecting components from the inventory on a first-in first-out (FIFO) basis. This results in a random combination of insertion losses in the assembled amplifier. If the random selection results in a sufficient number of component losses on the lower half of the bell curve distribution, an acceptable amplifier may be obtained notwithstanding the presence of one or more components from the upper half of the bell curve. On the other hand, the random selection of too many components from the upper halves of the respective bell curves results in an amplifier which exceeds the loss budget. In practice, the randomness of the component selection results in a large number of unacceptable amplifiers, i.e., the resultant device yields are low.
Of course, it is possible to simply extract and assemble only those components from the lower half of the bell curve. However, this results in a supply of amplifiers which, on the whole, are overbuilt (in terms of insertion loss), as well as a large number of unused and wasted components, i.e., the utilization efficiency of the components is low.